The present invention relates to a telephoto-lens, particularly for focusing the whole system by moving a part of the rear lens group along the direction of the optical axis. A telephoto-lens so designed that the focusing is made by moving a movable lens group in the rear lens group having a negative refractive power instead of advancing the whole lens has been disclosed in U.S. Pat. No. 4,045,128. The telephoto-lens of this type has a lens barrel that is mechanically simple, light in weight and excellent in operability, while at the same time the compensation of aberrations is difficult because a part of the lens group is moved. Particularly, in the case of a large aperture lens, the aberration can not be corrected sufficiently. Hereby it is to be mentioned that the F-number of the examples of the lenses in the above mentioned patent is 1:4.5.